# Fuel Cell vs. Electrolysis

1. Apr 11, 2010

Hey folks,

I am currently doing some research on hydrogen fuel cells as part of a project. I just wanted to clear up some confusion I am having with the whole *platinum issue.*

Very generally speaking, this is what I have gathered on H2 Fuel cell vehicles:

1) Electrolysis is needed to split water into hydrogen and oxygen, the former being used for fuel.

2) Somehow the H2 is used to reverse the electrolysis procedure to produce current to drive vehicle.

So for starters, we are not "burning" the hydrogen right? We are using an electrochemical system to drive the vehicle as opposed to a thermomechanical one?

Also, I keep getting confused as to where all if this platinum is being used? Is it in the electrolysis part when producing the hydrogen? Or is it on board in the vehicle while converting the H2 into a current? Or both? I ask because I keep finding loose references to the *platinum issue* in both areas (fuel cells and electrolysis).

So where does all the platinum come into play?

Thanks

2. Apr 11, 2010

### Topher925

Yes, there is no "burning" of the hydrogen. There is still a red-ox reaction occurring, just in a different manner. In a nut shell, the hydrogen ions and the electrons are spatially separated and are used to create electrical work. In a thermal engine the hydrogen ions and electrons roam about as they will and combine with oxygen to generate heat, used to drive the engine.

The platinum is used as a catalyst for both the hydrogen oxidation and the oxygen reduction reactions. It is located on the surface of the electrodes, which are usually made out of an activated carbon bonded to the polymer electrolyte (if we're talking PEMFCs).

For fuel cells, the platinum comes into play because it works as a great catalyst and allows the H2/O2 reaction to occur spontaneously and efficiently. With no catalyst there would be no reaction unless the cell operated at VERY high temperatures.

For electrolyzers, you really don't need any platinum or any type of catalyst at all. If you put a large enough voltage across water with an electrolyte mixed in, theres going to be H2 on one side and O2 on the other. The reason the platinum is there is because it makes the reaction more efficient. In other words it means you can generate more hydrogen for less electricity so in most cases it pays off to have it in there.

3. Apr 21, 2010

### Hologram0110

Also to add to what Topher925 said...
The platinum content is only an issue because it is a precious metal. It works great but is incredibly expensive, about $1700 per ounce, so it adds significantly to the cost of the fuel cell. A lot of fuel cell research is based on finding different catalysts not based on precious metals so the product might be commercially viable. 4. Apr 21, 2010 ### Topher925 About$1734 as of this morning and climbing.

If anyone cares (which no one but me probably does) there was recently a major breakthrough in catalyst research using a N based complex for catalyzing oxygen reduction reactions.

http://www.sciencemag.org/cgi/content/abstract/324/5923/71